What causes "Videos list cannot be empty" in ATH-MaaS/Pixelle-Video?

Check that the videos list is non-empty before calling concat_videos and handle the empty case explicitly (skip the step, or raise a domain-specific error).

ATH-MaaS/Pixelle-Video · error · ValueError

Videos list cannot be empty

Error message

Videos list cannot be empty

What it means

concat_videos validates its input before doing any work: an empty list of video paths cannot produce a concatenation, so it raises ValueError immediately (after _ensure_ffmpeg). This is a caller-contract error, not an FFmpeg failure.

Source

Thrown at pixelle_video/services/video.py:132

        bgm_volume: float = 0.2,
        bgm_mode: Literal["once", "loop"] = "loop"
    ) -> str:
        """
        Concatenate multiple videos into one

        Args:
            videos: List of video file paths to concatenate
            output: Output video file path
            method: Concatenation method
                - "demuxer": Fast, no re-encoding (requires identical formats)
                - "filter": Slower but handles different formats
            bgm_path: Background music file path (optional)
                - None: No BGM
        """
        self._ensure_ffmpeg()

        if not videos:
            raise ValueError("Videos list cannot be empty")
        
        if len(videos) == 1:
            logger.info(f"Only one video provided, copying to {output}")
            shutil.copy(videos[0], output)
            return output
        
        logger.info(f"Concatenating {len(videos)} videos using {method} method")
        
        # Step 1: Concatenate videos
        if bgm_path:
            # If BGM needed, concatenate to temp file first
            temp_output = output.replace('.mp4', '_no_bgm.mp4')
            concat_result = self._concat_demuxer(videos, temp_output) if method == "demuxer" else self._concat_filter(videos, temp_output)
            
            # Step 2: Add BGM
            logger.info(f"Adding BGM: {bgm_path} (volume={bgm_volume}, mode={bgm_mode})")
            final_result = self._add_bgm_to_video(
                video=concat_result,

View on GitHub (pinned to 848b054e4f)

Solutions

Check that the videos list is non-empty before calling concat_videos and handle the empty case explicitly (skip the step, or raise a domain-specific error).
Fix the upstream generation/glob logic so at least one input video exists.
If a single video is intended, pass it anyway — the method handles len==1 by copying it to output.

Example fix

// before
service.concat_videos(segments, 'final.mp4')  # ValueError if segments == []
// after
if not segments:
    raise ValueError(f'No video segments produced in {segments_dir}')
service.concat_videos(segments, 'final.mp4')

Defensive patterns

Strategy: validation

Validate before calling

if not videos:
    raise ValueError('No videos to concatenate')
for v in videos:
    if not os.path.isfile(v):
        raise FileNotFoundError(v)

Type guard

def is_nonempty_file_list(videos: object) -> bool:
    return isinstance(videos, list) and len(videos) > 0 and all(isinstance(v, str) and os.path.isfile(v) for v in videos)

Try / catch

try:
    service.concat_videos(videos, out)
except ValueError as e:
    if 'empty' in str(e):
        logger.warning('No segments produced; skipping concat')
        return None
    raise

Prevention

Guard the list for emptiness at the pipeline boundary before calling concat_videos.
Check upstream generation steps: if all segment creation failed, stop early with a clear message.
Log the number of segments before concatenation to catch silently-empty lists.
Prefer passing a single video rather than special-casing around the empty case.

When it happens

Trigger: Calling concat_videos([]) or passing a list that ended up empty because an upstream filtering step removed all candidate files (e.g. glob matched nothing, all files failed validation).

Common situations: Dynamic pipelines where segments are generated conditionally and all generation steps failed; glob patterns with wrong extensions returning no matches; refactored code that now returns a list instead of a tuple and drops a default item.

Related errors

AI-assisted analysis of ATH-MaaS/Pixelle-Video@848b054e4f (2026-08-30). Data as JSON: /api/errors/d20571811c4c0abc. Report an issue: GitHub.